Bitcoin, the contentious online currency, has been grabbing headlines lately, but the idea of spending digital money is still a novel one.

Greenwich resident John Dolan hopes it won't be for too long. Dolan, chair of the SolarCoin Foundation, along with a group of like-minded individuals loosely termed volunteers, is investing time and energy in SolarCoin, a virtual currency that strives to incentivize the solar energy industry.

Much like Bitcoin, SolarCoin is a currency that exists solely online, to be transferred from person to person or business to business through digital wallets. Where SolarCoin largely differs from the so-far controversial Bitcoin is in its purpose; the idea is not just to get people trading money online, but to encourage the use of solar energy. SolarCoin is an energy-backed currency, with one megawatt hour of solar energy equal to one SolarCoin. Once the system is fully operational, the idea is that anyone with a solar energy system will be able to automatically accumulate SolarCoins just by using energy, though the coin is intended for general use as well, not only for those with solar panels. Businesses and other organizations can download a digital wallet, locate the SolarCoin application and display a QR code on their website that announces SolarCoins will be accepted.

Though digital currency is an up-to-the-minute technology, Dolan and his fellow volunteers are thinking longterm: over the next 40 years, 99 percent of SolarCoins will go to solar energy generators.

Of course, SolarCoins -- and the idea of digital currency -- are still in very early stages. But Dolan is excited about the way that SolarCoins can bring two passionate groups of people together: those who believe strongly in renewable energy and those who see digital currency as the inevitable future.

"What we've done is the intersection of two neat worlds," Dolan said. "For those who want to make a statement about renewable energy, it's our hope they see these coins as a way to support the work of charities and other foundations."

So far, SolarCoin has garnered some local support: Solarize Greenwich, an outreach effort to popularize solar energy, is a fan of the currency, Dolan said. But, a large share of the enthusiasm for SolarCoin is coming from abroad. Dolan and other SolarCoin volunteers, including adviser Charles Moore and volunteer Nick Gogerty, are trying to orchestrate connections in Europe and Asia.

"I see a lot of transactional value [for digital currency] in developing economies where people are getting access to the internet and mobile phones before they have a bank account," Moore said. "I see that as a huge area for growth."

Although technology evolves rapidly, the fundamental logic of currency still applies: digital coins need a wide enough network of people who accept and use them in order to obtain value.

"If people buy into it, then it has value," Tucker said. "But, it's not like other collectibles because you can't touch it. We could make that leap in theory, as an international currency, but it can't happen that fast."